DESCRIPTION

The VOP_OPEN() entry point is called before a file is accessed by a
process and the VOP_CLOSE() entry point is called after a file is
finished with by the process.
The arguments are:
vp The vnode of the file.
mode The access mode required by the calling process.
td The thread which is accessing the file.
fp The file being opened.
Pointer to the file fp is useful for file systems which require such
information, e.g., fdescfs(5). Use ‘NULL’ as fp argument to VOP_OPEN()
for in-kernel opens.
The access mode is a set of flags, including FREAD, FWRITE, O_NONBLOCK,
O_APPEND.

LOCKS

VOP_OPEN() expects vp to be locked on entry and will leave it locked on
return.
VOP_CLOSE() expects at least a reference to be associated with the vnode
and does not care whether the vnode is locked or not. The lock and
reference state is left unchanged on return. Note that vn_close expects
an unlocked, referenced vnode and will dereference the vnode prior to
returning.